1. Field of the Invention
The present invention relates to spin-valve thin-film magnetic elements, thin-film magnetic heads, floating magnetic heads, and methods for making the spin-valve thin-film magnetic elements. In particular, the present invention relates to a technology for preventing a sensing current shunt in a spin-valve thin-film magnetic element in order to reduce side reading.
2. Description of the Related Art
Spin-valve thin-film magnetic elements are a type of giant magnetoresistive element (GMR) exhibiting a giant magnetoresistive effect and detecting recording magnetic fields from recording media such as a hard disk.
The spin-valve thin-film magnetic elements have relatively simple structures and high rates of changes in resistance to external magnetic fields and exhibit high sensitivity to weak magnetic fields.
FIG. 19 is a cross-sectional view of a conventional dual spin-valve thin-film magnetic element viewed from the air-bearing surface (ABS) which faces a recording medium. In this element, a nonmagnetic conductive layer, a pinned magnetic layer, and an antiferromagnetic layer are deposited on each of two sides of a free magnetic layer. In FIG. 19, the recording medium such as a hard disk moves in the Z direction and generates a leakage magnetic field in the Y direction.
The conventional spin-valve thin-film magnetic element 301 shown in FIG. 19 includes a substrate 302 and a laminate 312 formed on the substrate 302. The laminate 312 includes an underlayer 303 composed of Ta or the like, a first antiferromagnetic layer 304, a first pinned magnetic layer 305, a first nonmagnetic conductive layer 306 composed of Cu or the like, a free magnetic layer 307, a second nonmagnetic conductive layer 308 composed of Cu or the like, a second pinned magnetic layer 309, a second antiferromagnetic layer 310, and a protective film 311 from the bottom. A pair of hard bias layers 332 is formed on both sides of the laminate 312, and a pair of lead layers 334 is formed on the hard bias layers 332. The hard bias layers 332 are composed of a CoPt alloy or the like and the lead layers 334 are composed of Cu or the like.
The first pinned magnetic layer 305 is a laminate of a first pinned ferromagnetic sublayer 305a, a first nonmagnetic interlayer 305b, and a second pinned ferromagnetic sublayer 305c. The second pinned ferromagnetic sublayer 305c is thicker than the first pinned ferromagnetic sublayer 305a. 
The first pinned ferromagnetic sublayer 305a is magnetically coupled with the first antiferromagnetic layer 304. Thus, the magnetic moment of the first pinned ferromagnetic sublayer 305a is pinned in the Y direction. Furthermore, the second pinned ferromagnetic sublayer 305c is antiferromagnetically coupled with the first pinned ferromagnetic sublayer 305a. Thus, the magnetic moment of the second pinned ferromagnetic sublayer 305c is pinned in the opposite direction of the Y direction.
As described above, the magnetic moments of the first pinned ferromagnetic sublayer 305a and the first nonmagnetic interlayer 305b are antiparallel and mutually counteract each other. Since the second pinned ferromagnetic sublayer 305c is thicker than the first pinned ferromagnetic sublayer 305a, a small magnetic moment remains in the second pinned ferromagnetic sublayer 305c. Thus, the overall magnetic moment of the first pinned magnetic layer 305 is pinned in the opposite direction of the Y direction in the drawing.
The second pinned magnetic layer 309 is a laminate of a third pinned ferromagnetic sublayer 309a, a second nonmagnetic interlayer 309b, and a fourth pinned ferromagnetic sublayer 309c. The third pinned ferromagnetic sublayer 309a is thicker than the fourth pinned ferromagnetic sublayer 309c. 
The fourth pinned ferromagnetic sublayer 309c is magnetically coupled with the second antiferromagnetic layer 310. Thus, the magnetic moment of the fourth pinned ferromagnetic sublayer 309c is pinned in the opposite direction of the Y direction. Furthermore, the third pinned ferromagnetic sublayer 309a is antiferromagnetically coupled with the fourth pinned ferromagnetic sublayer 309c. Thus, the magnetic moment of the third pinned ferromagnetic sublayer 309a is pinned in the Y direction.
The magnetic moment of the third pinned ferromagnetic sublayer 309a and the magnetic moment of the fourth pinned ferromagnetic sublayer 309c also mutually counteract each other in the second pinned magnetic layer 309. Since the third pinned ferromagnetic sublayer 309a is thicker than the fourth pinned ferromagnetic sublayer 309c, a magnetic moment remains in the third pinned ferromagnetic sublayer 309a. Thus, the overall magnetic moment of the second pinned magnetic layer 309 is pinned in the Y direction in the drawing.
The first pinned ferromagnetic sublayer 305a and the second pinned ferromagnetic sublayer 305c in the first pinned magnetic layer 305 and the third pinned ferromagnetic sublayer 309a and the fourth pinned ferromagnetic sublayer 309c in the second pinned magnetic layer 309 are antiferromagnetically coupled with each other. Moreover, each of the second pinned ferromagnetic sublayer 305c and the third pinned ferromagnetic sublayer 309a has a residual magnetic moment. Accordingly, the first pinned magnetic layer 305 and the second pinned magnetic layer 309 exhibit a synthetic ferrimagnetic state.
The free magnetic layer 307 is a laminate of a first antidiffusion sublayer 307a composed of Co or the like, a free ferromagnetic layer 307b composed of a NiFe alloy, and a second antidiffusion sublayer 307c composed of Co or the like. The first antidiffusion sublayer 307a and the second antidiffusion sublayer 307c prevent mutual diffusion between the first nonmagnetic conductive layer 306 and the second nonmagnetic conductive layer 308.
The magnetic moment of the free magnetic layer 307 is oriented in the X1 direction (track width direction) in the drawing by a bias magnetic field from the hard bias layers 332. Accordingly, the magnetic moment of the free magnetic layer 307 is substantially orthogonal to the magnetic moment of the first pinned magnetic layer 305 and the magnetic moment of the second pinned magnetic layer 309.
The lead layers 334 on the hard bias layers 332 extend from both sides to the center of the laminate 312 in the X1 direction (track width direction), and partly overhang on the both end portions of the laminate 312 in the track width direction to form overlay sections 334a thereof. These overlay sections 334a are distant from each other at a distance Tw on the laminate 312.
The first antiferromagnetic layer 304 extends towards both sides in the X1 direction (track width direction) compared to the first pinned magnetic layer 305 and the free magnetic layer 307 to form protrusions 304a. The protrusions 304a and the hard bias layers 332 are separated by bias underlayers 331 composed of Ta, W, or Cr. The hard bias layers 332 and the lead layers 334 are separated by interlayers 333 composed of Ta, W, or Cr.
In this spin-valve thin-film magnetic element 301, the lead layers 334 supply a sensing current to the laminate 312. The magnetic moment of the free magnetic layer 307 varies from the X1 direction to the Y direction in response to a leakage magnetic field in the Y direction from a magnetic recording medium. The electrical resistance of the element changes in connection with the relationship between the change in the magnetic moment of the free magnetic layer 307 and the magnetic moments of the first and second pinned magnetic layer 305 and 309, respectively. This effect is called a magnetoresistive effect (MR effect). The leakage magnetic field from the magnetic recording medium is detected as a change in voltage caused by the change in electrical resistance.
In this spin-valve thin-film magnetic element 301, the sensing current primarily flows into the laminate 312 from the lead layers 334 via the vicinities of the edges 334b of the overlay sections 334a, as shown in FIG. 19. Thus, in the laminate 312, the sensing current is concentrated in the central region which is not covered by the overlay sections 334a. This central region, therefore, exhibits a noticeable MR effect and high detection sensitivity to the leakage magnetic field from the magnetic recording medium. This central region is referred to as a sensitive region S.
In contrast, in regions covered by the overlay sections 334a, the sensing current is extremely low compared with the sensitive region S. These regions exhibit a poor MR effect and thus low detection sensitivity to the leakage magnetic field. These regions are referred to as insensitive regions N.
As described above, the overlay sections 334a form the sensitive region S which contributes to reading the recording magnetic field from the magnetic recording medium and the insensitive regions N which do not contribute to the reading. The width Tw of the sensitive region S corresponds to the track width of the spin-valve thin-film magnetic element 301. In other words, the track width of the spin-valve thin-film magnetic element 301 can be reduced by providing the overlay sections 334a. 
In such a configuration, however, the sensing current includes a shunt component J2 which flows into the laminate 312 from the base portion 334c of one overlay section 334a and a shunt component J3 which flows into other layers at the substrate side from one lead layer 334 via the corresponding hard bias layer 332. These shunt currents J2 and J3 are not negligible.
These shunt currents J2 and J3 generate a change in magnetoresistance in the insensitive regions N. These insensitive regions N generate signals on the recording track of the magnetic recording medium.
When the width of the recording tracks and the distance between the recording tracks are reduced to increase recording density, side reading in which signals on the adjoining recording tracks are read out occurs during reading the signals which are read out in the sensitive region S. Such side reading may adversely affect as noise to the output signal and may produce erroneous results.
Furthermore, essential requirements for spin-valve thin-film magnetic elements are improvements in output characteristics and sensitivity.